I think you're overlooking the work and talent that goes into producing this (Emmy Award-winning) show. Here is an excerpt from an article that takes a look at the behind-the-scenes routine to making a typical episode:
For the next hour, Stewart paces diagonally across a windowless eight-by-eight-foot room, sucking on an iced coffee and grabbing handfuls of candy. Projected in front of him on one wall is the current script; beneath it, at two keyboards, sit Kristen Everman, a production assistant, and Kira Klang Hopf, an indefatigable senior producer. Head writer Steve Bodow and executive producers Josh Lieb and Rory Albanese perch on small couches. As the studio audience files into its seats down the hall and tonight’s musical guests, Arcade Fire, tune their guitars in the greenroom, Stewart and his team go on a nonstop, rapid-fire jag that tears up and rewrites nearly three-quarters of the script. The typist transcribes, cuts, and pastes; as visual gags pop feverishly into Stewart’s brain, Hopf calls down to the art department, ordering up new video montages and a collage of an “Anchor-Me Terror Baby” to go with a reference to the “birthright citizenship” debate. Many of the new ideas will be scrapped only moments later. ... As Stewart speeds along, hours of work by writers and producers are cut, replaced by improvised digressions.
http://nymag.com/arts/tv/profiles/68086/index4.html